Richard and Mayumi Heene, who allegedly fabricated the stunt in a bid to land their own reality television show, spoke quietly as they entered their pleas before a packed court-room at Larimer County Court.

Richard Heene, 48, pleaded guilty to a felony charge of attempting to influence a public servant while Mayumi, 45, a Japanese national, admitted a misdemeanor offense of false reporting to authorities.

Although the charges are punishable by jail terms of 90 and 60 days, respectively, the couple are expected to receive probation as part of a plea deal with prosecutors.

The Heenes will be sentenced Dec. 23, Judge Stephen Schapanski ruled during a morning hearing at the court in Fort Collins, outside Denver.

The couple could also be faced with a bill running into tens of thousands of dollars for the multi-agency search-and-rescue effort that took place after they reported that their 6-year-old son had accidentally floated away on a home-made balloon shaped like a flying saucer.

The child was later discovered hiding at home. Police said the incident had been a hoax designed by the Heenes to help them obtain a television deal.

The family's lawyer, David Lane, said in a statement Thursday that the couple agreed to the plea deal to prevent the possibility of Japan-born Mayumi being deported from the United States if convicted.

Although Mayumi Heene had admitted the hoax under questioning by Colorado investigators, she could not have been forced to testify against her husband, and her confession would have been inadmissible as evidence, Lane said.

That scenario created the possibility that Mayumi could have been convicted and deported while her husband might have been acquitted, Lane said.

"This however would have put the family at grave risk of seeing a loving, caring, compassionate wife and mother ripped from the family and deported," Lane said.